1. Field of the Invention
This invention relates to an endosseous implant embedded in the bone tissue of a living being for use in restoring the organic functions of the being, and more particularly to an implant having a polycapillary structure by being set in the alveolar bone for use in dental prosthesis and orthopedic surgery.
2. Prior Art
Along with the development of bioengineering and development of biomaterials, a therapeutic operation is practiced for embedding in the bone tissue an implant in the form of an artificial tooth root and artificial bone in the dental treatment and orthopedic surgery fields. It is said of the prosthetic materials used in a living being that metal materials or ceramic materials least related to the bio-system are higer in stability rather than high-molecular materials having a molecular structure similar to materials constituting the living being. Furthermore, it is required of prosthetic materials for use in the living being that the materials have no irritating or toxic effect on the cells and tissues, that they make no physical and chemical changes in the living body, especially no change in mechanical strength, that they can sufficiently stand external force, and that they are excellent in adhesibility with respect to their adjacent tissues.
Included under the biomaterials that can approximately satisfy the items of requirement mentioned above are metals such as pure aurum, platinum, titanium zirconium, tantalum, auric alloy, platinic alloy, titanic alloy, zirconic alloy, cobalt-chromic alloy, ferro-nickel-chromic alloy; and ceramic materials such as aluminum oxide, zirconium dioxide, silicon nitride, apatite crystallized glass. Various proposals have been made for making an implant of a composite material of the mentioned metals and/or ceramics to make reliable fixation of the implant in bone tissue. For example, in a dental endosseous implant used as an artificial tooth root, maintenance and anchoring of the implant in the alveolar bone depends greatly upon how the bone tissue, osteoid tissue and fibrous tissue are connected with the implant surface. As a result, a blade type implant has been formed with metallic or ceramic plate with vent holes each having a uniform size called a vent and designed to maintain the implant in the alveolar bone by the anchoring effect of a bone tissue proliferating and penetrating into the vents. Also, in a porous implant in which a porous ceramic material, cement material, or a sintered body of pure titanium and a titanic alloy is used as a material, retentive force of the implant in alveolar bone tissue is achieved by an anchor-hold created between the implant and the bone tissue in growth into the pores. For example, U.S. Pat. No. 4,259,072 to the previous invention of an endosseous ceramic implant by Dr. Haruyuki Kawahara, one of the present inventors is the case in point. According to the previous invention, the implant is a composite structure made, in combination, of an outer ceramic member and an inner ceramic core member, the outer member being made of porous ceramics and being formed both on the upside and on the underside with apertures of 20-50 .mu.m (for dental use) and being formed inside of the thickness thereof with net-like roots communicating with the apertures. A bone tissue and a connective tissue invade and pass through the apertures into the roots inside the member, with result that the outer member is stably maintained and anchored by an anchoring effect in the bone.
But the implants formed of conventionally known metals or alloys or ceramics, for example, a blade vent type and a corevent type implant have a hole of .phi. 1 mm or more and accordingly the implant is maintained only by the anchoring effect of the ingrowth bone tissue. But when this bone tissue is broken or damaged by a pathological cause or masticatory impact or concentration of masticatory stress, there are not a few cases bringing artificial tooth root into failure.
Also, because conventional porous implants are fragile in mechanical strength and the embedding portions of the implants are all columnar, the implants are restricted in the selection of the cases of which the use of the implant is effective and are small in the number of applications of the implants in compliance with the cases of disease.
Furthermore, since the outer member of the prior art U.S. Pat. No. 4,259,072, as previously mentioned, is obtained from porous ceramics, apertures and net-like roots are all formed of the porous structure alone, namely, the shape, size and distribution of the apertures and net-like roots are dependent upon the kind, amount of foaming agent used in forming pores and upon the sintering conditions of ceramics. Accordingly, the problem is that it is difficult in point of design to artificially control the desired shape, size and distribution of tubular channels.
In an attempt to solve the problems of the prior art, the present inventors make the following proposal by the invention they have made out after intensive research.